Integrin-specific signaling is likely to determine whether cell adhesion to the matrix promotes cell proliferation or exit from the cell cycle and differentiation. We have observed that a subset of beta1 and alphav integrins recruit the adaptor protein Shc by an indirect mechanism. The oligomeric membrane protein caveolin-1 appears to function in this pathway as an adaptor, which couples the transmembrane segment of the integrin alpha subunit to Fyn or Yes. Upon integrin-mediated activation, the Src kinase interacts, through its SH-3 domain, with Shc. Shc is then phosphorylated at Tyr 317 and activates Ras-ERK signaling. Our recent studies indicate that in endothelial cells the Shc-linked integrins and growth factor receptors cooperate to recruit SOS at sites of integrin-mediated adhesion and to increase its GEF activity toward Rac. Upon activation, Rac promotes translation of the Cyclin D mRNA, thus initiating the cell cycle events necessary for progression through G1. Although adhesion mediated by other integrins allows efficient activation of ERK and transcription of Cyclin D, it does not induce activation of Rac, translation of Cyclin D, and progression through G1. The major goal of this application is to uncover the signaling mechanisms by which Shc-linked integrins and growth factor receptors cooperate to promote, through Rac, translation of Cyclin D and possibly other mRNAs necessary for cell growth and cell division. Based on the observation that caveolin-1 is phosphorylated at Tyr 14 in response to joint integrin/growth factor receptor signaling, we will use caveolin- 1-/- cells reconstituted with wild type or Y14F caveolin-1 to examine the mechanism and biological consequences of this event. In addition, we will study the role of caveolin-1 in Src-dependent mammary oncogenesis by introducing the caveolin-14 mutation in transgenic mice engineered to express the Polyoma Middle T Antigen in the mammary gland. We will then examine the mechanisms by which alpha5beta1 associates with the EGF-R and alphavbeta3 combines with the PDGF-R. Emphasis will be placed on the potential role of uPAR, caveolin-1, Src kinases, and Shc. To gain insight into the integrin-specificity of signaling, we will examine the role of RPTP-alpha in Shc signaling. In addition, we will explore the possibility that the Shc-linked integrins, but not other integrins, associate with growth factor receptors. Finally, we will examine the mechanism by which Rac promotes CAP-dependent translation of Cyclin D. DNA microarray analysis of polysome-bound mRNAs will be employed to study the role that matrix control of mRNA translation plays in coordinating cell growth and cell division.